Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel delivery uses a port injector for each cylinder to deliver fuel to respective cylinders. Still another type of fuel delivery uses a direct injector for each cylinder.
Engines have been described utilizing multiple injector locations with different fuel types. One example is described in the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. Specifically, the Heywood et al. papers describes directly injecting ethanol to improve charge cooling effects, while relying on port injected gasoline for providing the majority of combusted fuel over a drive cycle.
However, the inventors herein have recognized several issues with such systems. For example, ethanol and gasoline have different power densities and different stoichiometric air-fuel ratios. Thus, if the absolute and relative amounts of fuel are varied with operating conditions during engine operation, combustion air-fuel ratio may inadvertently swing lean or rich during such operation. Further, engine torque may be affected as well since due to the different power densities of the fuels. As such, degraded emissions and driver comfort may be achieved.
Thus, in one approach, a system for an engine is provided, the system comprising: a cylinder located in the engine; a first injector for injecting a first fuel into said cylinder; a second injector for injecting a second fuel into said cylinder; and a controller configured to vary an amount of said first and second fuel injection during engine operation based on operating conditions, where amounts of variation of said first and second fuels are set to maintain desired engine output and provide a substantially stoichiometric mixture.
In this way, it is possible to enable continuous variation between absolute and relative amounts of fuel from different sources with variation in operating conditions, while maintaining a desired air-fuel ratio and engine output torque.
In one particular approach, the controller varies said amounts of one of said first and second fuel injection with a fuel blend of one or said first and second fuels. In this way, it is possible to maintain accurate air-fuel ratio control by compensating the amount of fuel injections based on the blend.
In another approach a system for an engine is provided, the system comprising: a cylinder located in the engine; a first injector for injecting a first fuel into said cylinder; and a second injector for injecting a second fuel into said cylinder, said second injector sized different than said first injector.
In this way, it is possible to utilize different fuel types with different power densities, yet still provide maximum engine torque and/or minimum engine torque with either fuel.